Fly Guys made their debut in Super Mario World 2: Yoshi's Island and has become a common enemy in later Mario and Yoshi games. They fly around and carry items, including 1-Ups and rare Red Coins. Some of them fly back and forth in a set path, while others appear suddenly, move quickly and fly away if not hit in time.
Propeller Shy Guys only appeared in Yoshi's Story. They appear flying above Yoshi carrying fruit, but immediately fly off-screen if Yoshi eats the fruit.
A Propeller Fly Guy as it appears in Yoshi's Story.
Despite the trophy name and description referring to Shy Guys in general, three Propeller Shy Guys are the only Shy Guys visually represented by the trophy.
There are many types of Shy Guys: they've been known to walk on the ground, fly through the air, traipse about on stilts, wear flowers or camouflage, throw balls, swing balls, swing bats, sail on pirate ships, carry fruit, do the Bamboo Dance, ride submarines, play guitar, play tennis, wear red, come in large or small sizes, steal people's toys, cause mischief...
Fly Guys appear as rare, harmless enemies. They fly around carrying an item which changes every few seconds, and if not defeated in time they quickly fly away. They can carry food, gold and Custom Parts, which they drop when attacked.
Three Fly Guys appear in one of the Survive! Hard Challenge rooms, carrying dangerous-to-get bonus loot.
This enemy from the Yoshi's Island series is basically a Shy Guy with a propeller on its head. It hauls items with it as it flies, so chase it down to claim a reward. Usually it's just food, but sometimes one will have some better prizes. You could say these ones are...pretty fly for a Shy Guy. No? Never mind.
This enemy usually appears in Yoshi's Island. It's basically a Shy Guy, but with a propeller on its head sooo...you could say it's pretty fly for a Shy Guy. No? OK, then. They fly around overhead with items that you'll want to get hold of! Usually it's only food, but just sometimes they might be carrying something even better...
Propeller Shy Guys return as background characters in the Super Happy Tree stage, while Fly Guys return and reprise their roles as a stage element in the Yoshi's Story and Yoshi's Island stages.